Single-Molecule Optomechanical Cycle

TLDR

Light‑powered molecular machines are thought to be essential components of future nanoscale devices. The authors synthesized a bistable azobenzene polymer and studied it with single‑molecule force spectroscopy combined with optical excitation in total internal reflection. The polymer could be optically lengthened and contracted, generating mechanical work against an external force, and was operated in a periodic mode to demonstrate optomechanical energy conversion at the single‑molecule level.

Abstract

Light-powered molecular machines are conjectured to be essential constituents of future nanoscale devices. As a model for such systems, we have synthesized a polymer of bistable photosensitive azobenzenes. Individual polymers were investigated by single-molecule force spectroscopy in combination with optical excitation in total internal reflection. We were able to optically lengthen and contract individual polymers by switching the azo groups between their trans and cis configurations. The polymer was found to contract against an external force acting along the polymer backbone, thus delivering mechanical work. As a proof of principle, the polymer was operated in a periodic mode, demonstrating for the first time optomechanical energy conversion in a single-molecule device.